iOSアプリでOAuth認証 ref: https://qiita.com/kfurue/items/276cd17a99ad75c2be37

file0.swift

    override func viewDidAppear(_ animated: Bool) {
        let keychain = Keychain(service: "kfurue.RxSwiftRailsTutorial-token")

        if keychain["oauthToken"] == nil {
            oauthswift.authorizeURLHandler = SafariURLHandler(viewController: self, oauthSwift: oauthswift)
            oauthswift.authorize(
                withCallbackURL: URL(string: "sample-app://oauth-callback")!,
                scope: "", state: "hoge",
                success: { credential, _, _ in
                    print(credential.oauthToken)
                    // OAuthSwiftで取得したトークンをKeychainにストアする
                    keychain["oauthToken"] = credential.oauthToken
            },
                failure: { error in
                    print(error.localizedDescription)
            }
            )
        }

    }

file1.swift

        let keychain = Keychain(service: "kfurue.RxSwiftRailsTutorial-token")

        guard let token = (try? keychain.get("oauthToken")) as? String else {
            return
        }

file2.swift

        SampleAppClientAPI.customHeaders["Authorization"]
            = "Bearer " + token
        feedTableView.register(UITableViewCell.self, forCellReuseIdentifier: "Cell")

        viewModel.feeds.asDriver().drive(
            feedTableView.rx.items(cellIdentifier: "Cell"),
            curriedArgument: {_, micropost, cell in
                cell.textLabel?.text = micropost.content
        }).disposed(by: disposeBag)